E. R. Seaquist

Physical Conditions of the Molecular Gas in Seyfert Galaxies

We examine the physical conditions of the global molecular gas reservoir in the host galaxies of Seyfert 1 and Seyfert 2 nuclei. To do so, we acquired sensitive 12CO,13CO, J = 1-0, and J = 2-1 observations and collected available data from the literature for a sample of 27 Seyfert galaxies. We find that Seyfert galaxies have an average value for the 12CO/13CO J = 1-0 and J = 2-1 line ratios of R10 = 12 and R21 = 13, respectively, with no discernible dependence on the Seyfert type. The r12 = (2-1)/(1-0) line ratio for 12CO does not reveal any significant difference between the two types, but Seyfert galaxies as a class seem to have systematically lower values of r12 (~0.5-0.7) than do average spirals and starbursts. Moreover, for all the galaxies examined, but especially for Seyfert and starburst galaxies, we find that r12 is likely to be smaller as the area of the galaxy sampled by the telescope beam becomes larger. This may be the consequence of a global gas excitation gradient in galaxies where warm (Tkin 20 K) gas lies confined, preferably in their central regions (1 kpc), while a colder (Tkin 10 K), and possibly subthermally excited, gas phase dominates the more extended CO emission in the disk. For Seyfert and starburst galaxies, there are indications that their gas excitation gradients may be quite similar. Examination of the properties of the molecular gas by using the r12, R10, and R21 line ratios reveals that, unless r12 0.6, a single warm gas phase can account for the observed values of these ratios toward the central regions of an average Seyfert and/or starburst galaxy.

EVIDENCE FOR RAM PRESSURE STRIPPING OF NGC-3073 BY OUTFLOWING GAS FROM NGC-3079

VLA H I observations in both C and D configurations have been made of the active galaxy NGC 3079 and its two companions NGC 3073 and MCG 9-17-9. The dwarf SO galaxy NGC 3073 is found to exhibit an elongated H I tail which is remarkably aligned with the nucleus of NGC 3079. Several scenarios are investigated as to the cause of the tail, including ram pressure and tidal effects. It is suggested that ram pressure due to outflowing gas from NGC 3079 is responsible for the H I tail. 27 references.

Nuclear jets in the radio lobe spiral galaxy, NGC 3079

The active, radio-lobe spiral galaxy NGC 3079 was observed, with the US VLBI network (plus Bonn), with successful detections on all baselines. The nucleus is found to consist of a binary source, along with a fainter, more extended component between the binary. The positions, sizes, and fluxes of each component are suggestive of jetlike outflow from a central compact object rather than of radio supernovae due to a starburst, and it is suggested that a nuclear jet is largely responsible for the kiloparsec scale outer radio lobes. 43 references.

Formaldehyde as a Tracer of Extragalactic Molecular Gas. I. Para-H2CO Emission from M82

Using the IRAM 30 m telescope and the 15 m JCMT, we explore the value of paraformaldehyde (p-H2CO) as a tracer of density and temperature of the molecular gas in external galaxies. The target of our observations are the lobes of the molecular ring around the center of the nearby prototypical starburst galaxy M82. It is shown that p-H2CO provides one of the rare direct molecular thermometers. Reproducing the measured line intensities with a large velocity gradient (LVG) model, we find densities of -->nH2 ~ 7 ? 103 cm ?3 and kinetic temperatures of -->Tkin ~ 200 K. The derived kinetic temperature is significantly higher than the dust temperature or the temperature deduced from ammonia (NH3) lines, but our results agree well with the properties of the high-excitation component seen in CO. We also present the serendipitous discovery of the -->42? 31 line of methanol (CH3OH) in the northeastern lobe, which shows?unlike CO and H2CO?significantly different line intensities in the two lobes.

OH Satellite Line Masers and an Active Galactic Nucleus Candidate in M82

We report the detection of OH satellite line masers at 1720 and 1612 MHz from the nuclear region of the starburst galaxy M82. The observations were aimed at detecting 1720 MHz maser emission from the known radio-emitting supernova remnant in the nuclear region. At 1720 MHz we detect six features above the 5 ? limit set by noise, four in emission and two in absorption. Three of the emission features appear closely associated with known discrete continuum radio sources, and one of the absorption features is precisely coincident with the discrete continuum source 44.01+59.6. The latter source also exhibits strong 1612 MHz emission at the same velocity. No other 1612 MHz features were detected. All of the 1720 MHz emission features are consistent with masers pumped by collisions with molecular hydrogen at densities between 103 and 105 cm-3 and Tk between 50 and 250 K. The absorption and emission associated with the two satellite lines in 44.01+59.6, together with other evidence, points to the possibility that this source is the active galactic nuclei in M82.

Gas and Dust in the Taffy Galaxies: UGC 12914/15

We present a comprehensive study of the dust and gas properties in the after-head-on-collision UGC 12914/15 galaxy system using multitransition CO data and SCUBA submillimeter continuum images at both 450 and 850 mu m. CO(3-2) line emission was detected in the disks of UGC 12914 and UGC 12915, as well as in a bridge connecting the two galaxies. Dust emission at 450 mu m was detected for the first time in the two galactic disks and in the connecting bridge. Using a large velocity gradient excitation analysis model we have obtained good estimates of the physical parameters in different regions of this system, and the amount of molecular gas was found to be 3-4 times lower than that estimated by other investigators using the standard Galactic CO-to-H-2 conversion factor. Comparing with the dust mass derived from the SCUBA data, we found that the gas-to-dust ratio was comparable to the Galactic value in the two galaxy disks but a factor of similar to 3 higher in the bridge. The physical condition of the molecular gas in the bridge is comparable to that in the diffuse clouds in our Galaxy. Our result is consistent with the scenario that the bridge molecular gas originated from the disk molecular clouds and has been drawn out of the galactic disks due to direct cloud-cloud collision. Our data indicate that the global star formation efficiency (SFE; L-IR/M-H2) in UGC 12915 is comparable to that of normal spiral galaxies, and the SFE is 40% lower in UGC 12914 than in UGC 12915. Little star formation activity was found in the bridge except in an H II region adjacent to the disk of UGC 12915.

Extended Dust Emission and Atomic Hydrogen: A Reservoir of Diffuse H2 in NGC 1068

We report on sensitive sub-mm imaging observations of the prototype Seyfert~2/starburst galaxy NGC 1068 at 850

Star Formation across the Taffy Bridge: UGC 12914/15

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Angular Expansion Measurement of the Young and Compact Planetary Nebula Vy 2-2

m and 450

OH Satellite-Line Masers in the Nucleus of NGC 253

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